Multifunctional integrated circuit chips are capable of providing two or more functions. Multifunctional chips often include a control circuit for selecting one of the functions. By selecting the appropriate function, the multifunctional chip becomes functionally identical to corresponding single-function chips. In this manner, multifunctional chips may replace various single-function chips. This flexibility can greatly reduce product development times and costs where each chip, whether multifunctional or single-function, requires a unique mask set.
Various techniques exist for selecting the desired function of a multifunctional chip. For instance, the multifunctional chip may be mounted on a customizable substrate, with the substrate customized to select the appropriate function. For instance, a laser beam may be used to selectively direct-write a met routing pattern on the substrate, or to selectively cut existing metallization on the substrate. Or, the leads of the substrate may be selectively coupled by appropriate jumper wires.
Connections between chips and substrates commonly performed by one of three technologies: wire bonding, controlled collapse chip connections (C4 or flip chip) and tape automated bonding (TAB). Typical wire bonds are gold or aluminum, and a typical wire bonding temperature is 225.degree. C. It may be desirable, for instance, to make a wire bond using a ball bond at the chip and a wedge bond at the substrate. Wire bonds provide a relatively low cost per connection and increase thermal dissipation from the chip.
Wire bonds have also been used to select the function of a multifunctional chip. For instance, a terminal may be wire bonded to a first bonding pad to select a first function, or to a second bonding pad to select a second function. Similarly, a bonding pad may be wire bonded to a first terminal to select a first function, or to a second terminal to select a second function. In either case, at least one terminal must be dedicated to selecting the chip function.
Multiple wire bonds are also known in the am In multiple wire bonds, separate wire bonds fan-out from a single terminal to multiple pads so that each pad is connected to the terminal by a separate wire bond. Thus, a single terminal may be double wire bonded to two bonding pads, triple wire bonded to three bonding pads, and so on. One purpose of multiple wire bonds is to reduce inductance. For instance, double wire bonds are used to couple a single power supply terminal to two adjacent bonding pads. A significant advantage of these double wire bonds is to reduce undesired inductive effects, such as noise and ground-bounce, that may arise in single wire bonds connected to power supply terminals.
Stitch bonding provides a convenient method of making double wire bonds. With stitch bonding, a wire is bonded to one of the bonding pads, then the wire is bonded to the terminal, then the wire is bonded to the second bonding pad, where the wire is then cut. This effectively provides a double wire bond with only one bonding operation.
A primary shortcoming and deficiency of the conventional approaches is the failure to teach a more versatile approach to using wire bonds for selecting various functions of a multifunctional chip.